On a small New Mexico dairy farm, an employee milking a cow does not have to be covered by workers’ compensation but the person’s supervisor, who might spend the workday in the same barn with the same animals, must be covered.

It’s a legal line that state Supreme Court justices hammered as they heard oral arguments Wednesday afternoon in a heated and possibly high-stakes case about a decades-old exemption in state law the allows farms and ranches with more than three employees to exempt laborers from workers’ compensation coverage.

A 2nd Judicial District Court judge and the Court of Appeals have ruled in one case that denying workers’ compensation to this type of farm and ranch worker is unconstitutional.

Dairy and ranch industry groups’ lawyers argued that forcing workers’ compensation coverage would cost farmers tens of millions of dollars, much of which they could not recoup from product sales, which usually are in markets that have government-set price controls.

When asked for the legal justification between the two groups of employees, like in the cow example, each of the industry lawyers arguing Wednesday struggled to find an answer that didn’t seem to anger the justices.

“It might save money by excluding certain workers, but is that a rational exclusion?” Chief Justice Charles Daniels asked the lead attorney representing the dairy and cattle industries.

Justices asked questions about how such an exemption could be considered constitutional.

Gail Evans, legal director for the New Mexico Center on Law and Poverty, argued that it is not and asked the justices to uphold a lower court’s ruling as such. She said those exempted are the “most vulnerable” employees.

She also asked that the justices make any unconstitutional judgment work retroactively.

But lawyers from the state’s Workers’ Compensation Administration and Uninsured Employer’s Fund argued that would open a flood gate of cases and a bureaucratic nightmare. They asked that if necessary, a ruling apply only to future claims to not only avoid a mess of back claims but also so that industry businesses can be fully aware of any new coverage requirement.

The coverage exemption also applies to household servants and real estate salespeople.

After more than two hours of arguments from five lawyers – oral arguments usually only last about one hour – before a packed and overflowing audience, justices took the case into consideration. It is not clear when they will make a decision.